1. Field of the Invention
The present invention is related to skis used for winter sports, and adapted to slide on snow and ice.
2. Discussion of Background and Relevant Information
Conventional skis normally comprise a lower sliding surface that is attached to two lateral surfaces along two lower edges equipped with metallic running edges, the lateral surfaces being joined at an upper surface. The width of the skis is relatively small with respect to their length, their front end being curved upwardly to form a spatula. The thickness of the ski is generally more substantial in the central portion than in the front and rear portions of the ski. In the conventional shapes that are used most often, the width of the lower surface of the ski is smaller in the central portion than in the rear and front portions, the width being maximum in the front portion of the ski, that is, in the vicinity of the spatula.
In known ski structures, the upper surface of the ski is generally an adjusted surface, that is, defined by the longitudinal displacement of a straight transverse line parallel to the lower surface of the ski. In other words, the transverse section of the ski is generally a rectangle or a trapezoid, the longer opposite sides of the rectangle or the trapezoid being formed by the lower surface and the upper surface of the ski, the smaller opposite sides of the rectangle or the trapezoid being formed by the lateral surface of the ski.
The greater thickness in the central portion of the ski confers this central portion with increased rigidity. This central zone is also adapted to receive the bindings that adapt to the user's boot. Conversely, the front and rear zones of the ski, that have lesser thickness, are more flexible, and apt to be elastically deformed when the ski is used. Should one wish to manufacture skis with good flexibility in the rear and front zones, one would have to necessarily provide that such front and rear zones have less thickness.
A first problem that arises in traditional ski structures is that the central zone of the ski, that has relatively greater thickness in order to confer it with greater rigidity, brings about a fairly substantial distancing of the bindings with respect to the lower edges of the ski. The lower edges are those elements that are adapted to bite into the ice while making a turn. The efficiency of the lower edges equipped with running edges is all the better when the connection between the foot of the user and the running edge is more direct. The distancing between the running edge and the binding tends to deteriorate the efficiency of the running edges.
A second problem that arises in known ski structures is that the substantial reduction of the thickness of the front and rear zones of the ski tends to substantially reduce the mass of these front and rear zones, and thus substantially reduces the inertia of the ski, both around a central vertical axis, and around a central horizontal axis, that are perpendicular to the longitudinal direction of the ski. The moment of inertia around the vertical axis, or the rotational axis of the ski, influences the behavior of the ski in rotation, by determining the resistance that the ski generates to a variation in the direction of the movement. A ski with a relatively small moment of inertia, for example, a short ski that is light at its ends, is easier to turn than a ski with a relatively large moment of inertia. But this reduction of the movement of inertia decreases the stability of the ski. Conversely, a ski with a relatively large moment of inertia is especially stable directionally during quick descent, because the stresses exercised laterally on the ski by the inequalities of the slope are better absorbed due to the greater moment of inertia. On the other hand, the moment of inertia around its central horizontal axis, perpendicular to the longitudinal direction of the ski influences the vibratory behavior of the ski. It is known that vibrations can be harmful and lead to a loss of adherence to the ground by the lower edges of the ski, and consequently, to a directional instability.